Alzheimer's disease (AD) is a neurodegenerative disease that affects approximately one-half of the U.S. population greater than 85 years of age. APOE2 is associated with a lower risk and delayed onset for AD. Numerous studies suggest a role of APOE2 in human longevity as shown by a strong association between the APOE2 allele and reduced aging-related cognitive decline. However, while most research effort in APOE and AD has been focused on detrimental effects of APOE4, very limited studies have addressed the protective effects of APOE2. Cellular mechanisms pertaining to A? clearance, neurofibrillary tangle burden, synaptogenesis and synaptic plasticity, glial activation, and neuro-inflammation have been proposed, but an in- depth molecular characterization of these effects in aging and AD has not been established, partially due to a low allele frequency of APOE2. For example, APOE2 has a much lower allele frequency than APOE3 and APOE4 alleles in pre-existing large-scale gene expression data sets of human postmortem brains (N?30 of APOE2 carriers in both non-demented controls and AD cohorts). This low allele frequency poses a significant challenge to identify molecular networks and drivers mediating APOE2 effects. To overcome this challenge, we propose to leverage pre-existing human brain data sets and integrate them with new data sets to be generated from additional human brain samples, ?2/?3 and ?2/?4 iPSC-derived brain cells (Aim 1) and EFAD animal models (Aim 2). After extensive quality control and covariate correction of the assembled data sets, we will perform integrative high-resolution network modeling analysis to identify multiscale molecular networks and key drivers mediating APOE2-specific protective effects against aging and AD (Aim 3). In this application, we propose to define how interactions with APOE3 and APOE4 alter the APOE2-MNs and functional read-outs characteristic of aging and AD-related pathology. We will also determine how sex affects these processes. We will also validate the key differences in APOE2-MNs using postmortem human brain samples, iPSC-derived brain cells and EFAD mouse brain tissue to confirm the biological relevance of the findings. We will then characterize the functional relevance of top key drivers of the most informative subnetworks of APOE2 using gene perturbation techniques in iPSC-derived brain cells and EFAD mice (Aim 4). All the data and models developed through this study will be shared with the community. Our proposed studies will systematically construct, characterize, and validate APOE2-specific MNs in context of interacting with other APOE alleles and sex that potentially impact longevity, learning and memory, as well as AD development and progression. We expect this work will facilitate identification and development of targeted therapeutic approaches to AD incorporating APOE genotype and sex, the basis of personalized medicine. Therefore, we expect the proposed research will help decrease the burden of this devastating disease and have a large impact on AD research.